Centerpoint drill grinding machine

ABSTRACT

A drill pointing machine has a grinding wheel with contiguous grinding surfaces to simultaneously grind a centerpoint cone and the flutes on a drill. A drill holder positions the drill with its central axis tipped with respect to the cone grinding surface and the held drill is advanced then retracted along a line parallel to the cone grinding surface as the drill is rotated and while infeeding.

[ Nov. 4, 1975 United States Patent [191 Caley 51/288 X 51/95 WH X 408/230 X 2,984,949 5/1961 Dayton.......................... 3,037,329 6/1962 Ernst 3,040,480 6/1962 Winslow.....

[73] Assignee: The Boeing Company, Seattle,

wash. Przmary ExammerAl Lawrence Smith Assistant Examiner-Nicholas P. Godici [22] Filed: Dec. 21, 1973 Attorney, Agent, or Firm-Morris A. Case; Glenn Orlob 21 Appl. No.: 427,387

ABSTRACT A drill pointing machine has a grinding wheel with contiguous grinding surfaces to simultaneously grind a centerpoint cone and the flutes on a drill. A drill holder positions the drill with its central axis tipped with respect to the cone grinding surface and the held drill is advanced then retracted along a line parallel to the cone grinding surface as the drill is rotated and while infeeding.

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US. Patent Nov. 4, 1975 Sheet 2 of2 3,916,570

ll All! CENTERPOINT DRILL GRINDING MACHINE BACKGROUND OF THE INVENTION It is known to grind a centerpoint tip on a drill as the point improves the accuracy of the drill. In U.S. Pat No. 3,040,480 a drill pointing machine grips and rotates a drill while oscillating toward and away from a grinding wheel and simultaneously the drill is moved laterally across and over the end of the grinding surface. US. Pat. No. 3,209,493 imparts an additional movement during grinding with the drill axis inclined at an angle to the surface during oscillation and lateral movement of the drill. The tip obtained from these machines has a raised feathered centerpoint that is more chisel shaped than pointed with a ridge extending at an angle across the width of the web. It is possible by using these or other known machines to vary the grinding parameters to obtain a feathered centerpoint with a pronounced point. It is known also to obtain a twist drill with a cone shaped centerpoint that has circular cross section. The drill is first ground in a machine to obtain a pronounced feathered centerpoint in the conventional manner. Next, a circular cone is ground on the feathered point being careful to limit the height of the cone to prevent contacting the previously ground cutting surfaces between the flutes. This leaves a land at the base of the cone which must be split on both sides. It was discovered that a centerpoint drill having a circular cross section may be machined in one operation that does not have the land.

SUMMARY OF THE INVENTION A drill is placed to rotate in a collet and indexed in a holder with a cutting edge of one of the flutes about vertical as the drill starts to move into contact with a grinding wheel. The grinding wheel has two contiguous grinding surfaces subtending an obtuse angle with a sharp line of demarcation therebetween. The drill is centered in a bushing extending near the drill point. The drill axis is canted with respect to one of the grinding surfaces and the drill is positioned and programed with a rectilinear oscillation to advance, retract, pause in the retracted position, then repeat the cycle. This cycle synchronizes with rotation of the drill to advance, retract and pause twice for each revolution of the drill. The reciprocating movement is along a line parallel to the cone grinding surface which grinds the cone at the same time as the flutes are being ground by the contiguous grinding surface.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a side elevational schematic view of the centerpoint grinding machine partly in section.

FIG. 2 shows a fragmented side elevational view of the grinding wheel and held drill of FIG. 1.

FIG. 3 shows a fragmented side elevational view as in FIG. 2 with another embodiment of the grinder.

FIG. 4 shows a graph illustrating drill linear movement during a grinding cycle.

FIG. 5 shows a fragmented end elevational sectional view taken along line 55 of FIG. 1.

DETAILED DESCRIPTION A drill holder assembly 10, see FIG. 1, has housing 12 which integrally connects to a member 14 by which the assembly is supported. A collet 16 has an outwardly extending pin 18 and adjustable chuck 20 for gripping a 2 drill 22. The collet inserts into a recess in bearing 24. The bearing has a projection 26 with slot 28 matched in size to contain the pin 18. Bushing 30 is positioned in the housing to be concentric to the drill axis. The bushing is preferably sized to a diameter that does not exceed the drill diameter by more than 0.0002 inch. The housing 12 has a radially extending offset projection 32 which supports bearing 34 and an offset 36. The two bearings are aligned with center axis parallel to each other and are synchronized to rotate in unison with bearing 34 rotating twice while bearing 24 rotates once. Helical spur gear 38 on bearing 24 and helical spur gear 39 on bearing 34 mesh together and are sized to obtain the desired relative rotational speeds. Bearing 34 supports axle or shaft 40 which is driven by a motor not shown. Cam 42 is located on the end of the axle and works in conjunction with cam follower 44. The cam follower has offset axle 46 which works in bushing 48 when turning arm 50 is rotated to in effect cancel the cam by moving the cam follower out of contact. Block 52 is slidably mounted on upright support 54 which in turn is fastened to frame 56. The block may be raised or lowered by worm screw 58 which meshes with and is driven by worm wheel 60. The worm screw meshes with threads in the block to raise or lower the block as the screw is rotated. The block supports the drill holder assembly 10. Support member 14 extends through the block and has raised ring 61. Compression spring 62 encircles the support member and works between the block and the ring to continually urge the drill holder toward the block. Zee member 64 has one leg 66 joined to the block. The zee member supports arm 68 which in turn contains bushing 48. Adjustment screw 70 extends through leg 72 of the zee member and has knurled head 74 for adjusting the screw so that its end 76 contacts offset 36 to limit the travel of the drill support members. The drill is ground by contacting wheel 78 which has contiguous grinding surfaces 80 and 82. These grinding surfaces subtend an obtuse angle and have a sharp line of demarcation 84. The drill as best shown in FIG. 2 has the central axis tipped upward with respect to top surface 80, with an angle of about 22 /2 preferred, and the height adjusted with the central axis tip 86 of the drill aligned along a line parallel to referenced surface 80. Whem cam action moves the drill into contact with the grinding wheel the drill advances along the same line parallel to referenced surface 80 and as shown best in FIG. 1, a cone 88 is ground by surface 80 and simultaneously flutes 90a and 90b are ground by grinding surface 82. The cam and cam follower provide movement and sequencing to grind the twist drill with a circular cross sectioned centerpoint cone and in this embodiment movement into contact and infeeding to determine the height of the cone is provided by moving the grinding wheel. The wheel is held between plates 92a and 92b with nut 94 which is fastened to the end of shaft 96. Shaft 96 extends through slide block 98 and is driven by a motor not shown. The sliding block is supported in parallel V shaped ways 100a and l00b. These ways are part of support 102 which is mounted on the frame 56. The sliding block is moved along a line parallel with the top grinding surface by infeed screw 104 which extends through reaction block 106 thence the sliding block 98 to move the block with grinder when wheel 108 is turned by handle 1 10. The forward travel of the grinding wheel is limited by the end 112 of adjustment screw 114 contacting ear 116 which is connected to support 3 102. Knurled head 118 is used to turn the screw in the sliding block. FIG. best shows the means for supporting the sliding block 98 in the ways 100a and l00b of the support structure 102. Gib 119 is used to hold the dovetailed parts in place and take up wear. The ways are aligned to be parallel to the grinding surface 80.

To set up, the drill 22 is placed in the collet 16 with the tip extending about one-half the diameter of the drill beyond the bushing 30. The drill is rotated until the leading or cutting edge of the flute is preferably about 12 past vertical position when the cam 42 is positioned to initiate forward movement of the held drill. The collet chuck 20 is tightened to hold and index the drill with the pin 18 resting in slot 28. The height of the drill holder assembly is set to grind cone 88 on grinding surface 80. The drill axis is tipped upward with respect to that referenced grinding surface to a predetermined position preferably at an angle of about 22 /2 to give a cone subtending an angle of about 45. The tip along the axis of the drill is positioned along a line extending from grinding surface 80. Thus when the drill is advanced along that same line the tip of the ground cone is on the drill center axis.

Adjustment screw 70 is set to limit retraction of the drill holder assembly as urged by the spring 62. Limiting this retraction in effect blocks out the cam 42 during part of its travel to give a cycle wherein the drill is advanced, retracted and held in the retracted position to impart a pause to its reciprocating movement. The duration of the pause may be thus varied. The length of the pause is matched to the degrees of width of the flute, and is varied within limits to obtain a true circular cross section of the cone and constant clearance angle on the ends of the flute. Too short a time of pause will cause the cone to be out of round, and too long a time of pause will cause an upturn on the heel of the clearance surface on the flutes. With the drill in the retracted position the driven grinding wheel is advanced to contact the drill. In operation shaft 40 is then driven to rotate the cam twice for each revolution of the drill. The grinding wheel infeeds to the desired depth of cone as determined by the travel limiting screw 1 14 acting in conjunction with stopping ear 116 and simultaneously grinds cone 88 on surface 80 and flutes 90a and 90b on surface 82. Preferably, handle 50 is then turned to move cam follower 44 away from the cam 42 to polish the cone with the drill rotating in the retracted position. FIG. 4 graphically shows the linear movement of the drill during one revolution cycle. Distance 120 shows the amplitude of drill movement which provides clearance on the flutes. Preferably, the cutting edge on one flute has rotated about 12 past vertical position when cam action starts at 122 to advance the drill into the grinding wheel. The drill advances and retracts in response to cam 42 and cam follower 44 interaction and retracting spring 62 until point 124 is reached at which point surface 76 on adjustment screw 70 limits the retraction until point 122a is reached.

A drill to be ground preferably has a web width that approximates the predetermined base diameter of the to be generated centerpoint cone. This width varies according to the drill size but preferably ranges from about 0.015 inch on a 3/16 inch drill to about 0.050 inch for a 1 inch drill. If wider web drills are used it is preferable to thin the web for a distance back from the point in a machine such as a Makino tool grinder with helical grinding attachment.

FIG. 3 shows an alternate embodiment with grinding wheel 126 with cone grinding surface 128 and flute grinding surface 130. The relative motion between the grinding wheel and the held drill and the direction of cam throw must as in the previous embodiment be parallel to the line of extension of the cone grinding surface 128.

I claim:

I. A drill pointing machine to impart a conic centerpoint, the combination comprising: a drill supporting structure, a driven grinding wheel having a pair of contiguous grinding surfaces subtending an obtuse angle at a sharp line of demarcation; means for providing relative movement between the drill and the grinding wheel along a line parallel with the topmost grinding surface; means for reciprocally advancing and retracting the drill along a line parallel to the topmost grinding surface with the drill held in a bushing at a predetermined angle to simultaneously grind the flutes and a circular cross sectional centerpoint cone on the end of the web, said means providing for an advance, a retraction, and a pause in the retracted position during each one-half of each revolution by the drill; means for holding the drill in the retracted position for final polish of the cone; and means for variably adjusting the duration of the pause.

2. A drill pointing machine for grinding a drill with a centerpoint cone in a single set up, the combination comprising: a driven wheel with two contiguous grinding surfaces subtending an obtuse angle having a sharp line of demarcation; a drill holder having a bushing to support adjacent the drill tip; means for providing relative movement between the held drill and the grinding wheel along a line parallel to one of the grinding surfaces; means for advancing the drill, held at a predetermined inclined drill axis angle, into the grinding wheel along a line parallel to the referenced grinding surface, and for reciprocally retracting the drill, said means timed to cycle an advance, retract and pause twice during one complete revolution of the drill and said drill predetermined position selected with respect to the line of demarcation between the grinding surfaces to simultaneously grind the centerpoint cone on the referenced grinding surface and the flutes on the other grinding surface; and means for adjustably controlling the advance, retract and pause cycle to extend or limit the length of time of the pause.

3. A drill pointing machine as in claim 2 further comprising means for holding the rotating drill in the retracted position with the side of the cone contacting the grinding surface to polish the cone.

4. A drill pointing machine for grinding a drill with a centerpoint cone in a single set up, the combination comprising: a holder allowing rotation of a drill, said holder having a nonrotating bushing to support the drill adjacent the tip, a driven cam synchronized with the held drill to rotate twice for each rotation of the drill, a cam follower cooperating with the cam to impart reciprocating movement to advance and retract the held drill, means for adjustably blocking out cam action during part of the cam travel to limit the retraction, a driven wheel with two contiguous grinding surfaces subtending an obtuse angle having a sharp line of demarcation, means for infeeding and retracting the grinding wheel and the drill point into and out of contact with each other with a rectilinear movement parallel to one of the grinding surfaces and to the cam driven movement, said grinding wheel contacting the drill at a predetermined height and angle to the drill axis to simultaneously grind the circular cross sectioned cone tip on the referenced grinding surface and the flutes on the other grinding surface in response to the cam driven movement.

5. A drill pointing machine as in claim 4 further comprising means for cancelling the cam for cone polishing with the drill rotating in the retracted position.

6. A drill pointing machine as in claim 5 wherein the referenced grinding surface is the top surface.

7. A drill pointing machine for grinding a drill with centerpoint cone in a single set up, the combination comprising: a driven wheel with two contiguous surfaces subtending an obtuse angle; a drill holder allowing rotation of a drill; means for advancing the drill, held at a predetermined inclined drill axis angle, into the grinding wheel along a line parallel to one of the 6 grinding surfaces and for reciprocally retracting the drill, said means for advancing and retracting the held drill comprises a cam acting in conjunction with a cam follower to move the drill holder, and timed to cycle an advance, retract and pause twice during one complete revolution of the drill, and said drill predetermined position selected to simultaneously grind the centerpoint cone on the referenced grinding surface and the flutes on the other grinding surface; means for advancing or retracting the grinding wheel towards the drill along a line parallel to the referenced grinding surface; and the means for creating a pause with the held drill in the retracted position is an adjustable stop located to limit retraction of the drill holder to in effect block out the cam during part of its travel. 

1. A drill pointing machine to impart a conic centerpoint, the combination comprising: a drill supporting structure, a driven grinding wheel having a pair of contiguous grinding surfaces subtending an obtuse angle at a sharp line of demarcation; means for providing relative movement between the drill and the grinding wheel along a line parallel with the topmost grinding surface; means for reciprocally advancing and retracting the drill along a line parallel to the topmost grinding surface with the drill held in a bushing at a predetermined angle to simultaneously grind the flutes and a circular cross sectional centerpoint cone on the end of the web, said means providing for an advance, a retraction, and a pause in the retracted position during each one-half of each revolution by the drill; means for holding the drill in the retracted position for final polish of the cone; and means for variably adjusting the duration of the pause.
 2. A drill pointing machine for grinding a drill with a centerpoint cone in a single set up, the combination comprising: a driven wheel with two contiguous grinding surfaces subtending an obtuse angle having a sharp line of demarcation; a drill holder having a bushing to support adjacent the drill tip; means for providing relative movement between the held drill and the grinding wheel along a line parallel to one of the grinding surfaces; means for advancing the drill, held at a predetermined inclined drill axis angle, into the grinding wheel along a line parallel to the referenced grinding surface, and for reciprocally retracting the drill, said means timed to cycle an advance, retract and pause twice during one complete revolution of the drill and said drill predetermined position selected with respect to the line of demarcation between the grinding surfaces to simultaneously grind the centerpoint cone on the referenced grinding surface and the flutes on the other grinding surface; and means for adjustably controlling the advance, retract and pause cycle to extend or limit the length of time of the pause.
 3. A drill pointing machine as in claim 2 further comprising means for holding the rotating drill in the retracted position with the side of the cone contacting the grinding surface to polish the cone.
 4. A drill pointing machine for grinding a drill with a centerpoint cone in a single set up, the combination comprising: a holder allowing rotation of a drill, said holder having a nonrotating bushing to support the drill adjacent the tip, a driven cam synchronized with the held drill to rotate twice for each rotation of the drill, a cam follower cooperating with the cam to impart reciprocating movement to advance and retract the held drill, means for adjustably blocking out cam action during part of the cam travel to limit the retraction, a driven wheel with two contiguous grinding surfaces subtending an obtuse angle having a sharp line of demarcation, means for infeeding and retracting the grinding wheel and the drill point into and out of contact with each other with a rectilinear movement parallel to one of the grinding surfaces and to the cam driven movement, said grinding wheel contacting the drill at a predetermined height and angle to the drill axis to simultaneously grind the circular cross sectioned cone tip on the referenced grinding surface and the flutes on the other grinding surface in response to the cam driven movement.
 5. A drill pointing machine as in claim 4 further comprising means for cancelling the cam for cone polishing with the drill rotating in the retracted position.
 6. A drill pointing machine as in claim 5 wherein the referenced grinding surface is the top surface.
 7. A drill pointing machine for grinding a drill with centerpoint cone in a single set up, the combination comprising: a driven wheel with two contiguous surfaces subtending an obtuse angle; a drill holder aLlowing rotation of a drill; means for advancing the drill, held at a predetermined inclined drill axis angle, into the grinding wheel along a line parallel to one of the grinding surfaces and for reciprocally retracting the drill, said means for advancing and retracting the held drill comprises a cam acting in conjunction with a cam follower to move the drill holder, and timed to cycle an advance, retract and pause twice during one complete revolution of the drill, and said drill predetermined position selected to simultaneously grind the centerpoint cone on the referenced grinding surface and the flutes on the other grinding surface; means for advancing or retracting the grinding wheel towards the drill along a line parallel to the referenced grinding surface; and the means for creating a pause with the held drill in the retracted position is an adjustable stop located to limit retraction of the drill holder to in effect block out the cam during part of its travel. 